JP2013014497A - Aqueous dispersion and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous dispersion which has high dispersibility of particles even when the concentration of the particles is high, and which has such high stability that precipitates are hardly formed even if it is stored for a long period of time and which has high transparency.SOLUTION: The aqueous dispersion includes particles formed from a rare earth phosphate and having a BET specific surface area of 10-200 m/g. The maximum particle diameter Dof the particles is 100 nm or less, the pH of the aqueous dispersion is ≥1 and <5, and the concentration of the particles is 5-50 mass%. Alternatively, the pH of the aqueous dispersion may be 9.1-14. It is preferable that the aqueous dispersion has a transmittance in a visible light wavelength region of 50% or more, as measured by using a cell having an optical path length of 1 cm.

Description

  The present invention relates to an aqueous dispersion containing particles comprising a rare earth phosphate and a method for producing the same. The aqueous dispersion liquid of the present invention is suitably used as a raw material for forming a thin film useful for various optical materials by drying it as a coating film.

  It is known that rare earth phosphate is a material having a high refractive index and Abbe number in the wavelength range from ultraviolet light to infrared light including the visible light wavelength region. Taking advantage of these characteristics, rare earth phosphates are used in various fields as optical materials.

For example, the techniques described in Patent Documents 1 and 2 are known as conventional techniques relating to an aqueous dispersion of a rare earth phosphate. Patent Document 1 describes an aqueous colloidal dispersion of isotropic particles of a rare earth element phosphate such as LaPO ₄ . This colloidal dispersion contains a complexing agent having a pK of 2.5 or more and a water-soluble monobasic anion having a pKa in the range of 2.5-5. Patent Document 2 describes a colloidal dispersion containing a rare earth phosphate such as LaPO ₄ and an anion of a water-soluble monobasic acid having a pKa of at least 2.5. This phosphate is anisotropic such as needle-like.

JP-T-2004-515433 JP-T-2004-525051

  The aqueous dispersions described in Patent Documents 1 and 2 have a low concentration of a solid content concentration of the rare earth phosphate contained therein of several percent at most. Therefore, when a thin film is produced by application of such an aqueous dispersion, it is necessary to apply the aqueous dispersion a plurality of times in order to form a thin film having a certain thickness, which takes time and effort.

  Accordingly, an object of the present invention is to provide an aqueous dispersion capable of easily forming a thin film useful in the field of optical materials.

The present invention relates to an aqueous dispersion containing particles comprising a rare earth phosphate having a BET specific surface area of 10 to 200 m ² / g, wherein the maximum particle diameter D _{max of the} particles is 100 nm or less, and the aqueous dispersion The above-mentioned problem is solved by providing an aqueous dispersion having a pH of 1 or more and less than 5 and a concentration of the particles of 5 to 50% by mass.

The present invention also provides a method for producing the aqueous dispersion as described above.
Disclosed is a method for producing an aqueous dispersion characterized by dispersing particles comprising a rare earth phosphate having a BET specific surface area of 10 to 200 m ² / g in an aqueous medium and adjusting the pH to 1 or more and less than 5. Is.

The present invention also provides an aqueous dispersion containing particles of rare earth phosphate having a BET specific surface area of 10 to 200 m ² / g, wherein the maximum particle diameter D _{max of the} particles is 100 nm or less, and the aqueous dispersion The above-mentioned problems are solved by providing an aqueous dispersion having a liquid pH of 9.1 to 14 and a concentration of the particles of 5 to 50% by mass.

The present invention is also a preferred method for producing the aqueous dispersion,
A method for producing an aqueous dispersion characterized by dispersing particles comprising a rare earth phosphate having a BET specific surface area of 10 to 200 m ² / g in an aqueous medium and adjusting the pH to 9.1 or more and 14 or less. It is to provide.

  The aqueous dispersion of the present invention has a high dispersibility of particles even at a high concentration, a high stability that does not easily generate a precipitate even after long-term storage, and a high transparency.

1 is an XRD diffractogram of lutetium phosphate particles obtained in Examples 1 to 5 and Comparative Example 1. FIG. FIGS. 2A to 2E are diagrams showing the reflectance of the lutetium phosphate particles obtained in Examples 1 to 5, respectively. 3 is a view showing a visible light transmission curve of the aqueous dispersion of Example 1. FIG. 4 is a view showing a visible light transmission curve of the aqueous dispersion of Example 6. FIG. FIG. 5 is a view showing a visible light transmission curve for the aqueous dispersion of Example 7. FIG. FIG. 6 is an XRD diffractogram of the rare earth phosphate particles obtained in Examples 9 to 12. 7 is a graph showing the reflectance of the ytterbium phosphate particles obtained in Example 9. FIG. FIG. 8 is a graph showing the reflectance of the yttrium phosphate particles obtained in Example 10. FIG. 9 is a graph showing the reflectance of gadolinium phosphate particles obtained in Example 11. FIG. 10 is a graph showing the reflectance of the lanthanum phosphate particles obtained in Example 12.

Hereinafter, the present invention will be described based on preferred embodiments thereof. The aqueous dispersion of the present invention comprises a rare earth phosphate represented by LnPO ₄ (Ln represents a rare earth element, hereinafter referred to as “Ln” in this sense) as a dispersoid using water as a medium. It contains particles. Since rare earth phosphate is generally a material having a high refractive index and a high Abbe number, the aqueous dispersion of the present invention containing such a material is suitable as a raw material for producing an optical material such as an optical lens. The aqueous dispersion of the present invention may contain one kind of rare earth phosphate or may contain two or more kinds as required. In addition, the phosphate mentioned in this specification is an orthophosphate. Orthophosphates, hydrogen phosphates and dihydrogen phosphates are known as orthophosphates, and the rare earth phosphates used in the present invention are orthophosphates.

The rare earth elements in the rare earth phosphate represented by LnPO ₄ include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. is there. Among these, since the refractive index and the Abbe number of the phosphate are particularly high, it is preferable to use a rare earth element selected from Y, La, Gd, Yb and Lu.

  The rare earth phosphate used in the present invention may be crystalline or amorphous (amorphous). When the rare earth phosphate is crystalline, the crystal system is preferably tetragonal or monoclinic from the viewpoint of advantageous optical characteristics.

  As for rare earth element phosphates, crystal structures of a xenotime structure, a monazite structure, and a rubbed phene structure are known. In general, when a phosphate mainly contains Lu, Yb, Y or the like, the phosphate has a tetragonal xenotime structure, and when mainly contains Gd or La, the phosphate has a monoclinic monazite structure. Further, when the rare earth element phosphate is a hydrate, it takes a hexagonal rubbed phene structure. When applying rare earth phosphates to optical lenses, it is often important to have a high refractive index. However, the rubbed ferne structure has a refractive index compared to other crystal structures due to the influence of water molecules. It is considered that the optical characteristics are disadvantageous such as low. Furthermore, in the case of a hydrate, there may be a problem with stability over time. For these reasons, the rare earth element phosphate preferably has a tetragonal or monoclinic crystal structure. The rare earth element phosphate may be amorphous instead of taking these crystal structures.

The aqueous dispersion of the present invention is characterized by a high concentration of the rare earth phosphate in addition to the above-mentioned rare earth phosphate. As will be described later, since the rare earth phosphate particles used in the present invention are fine particles, it is not easy to highly disperse such fine particles at a high concentration. It was surprisingly found that fine rare earth phosphate particles can be highly dispersed at a high concentration by using one having a specific BET specific surface area. Specifically, in the present invention, rare earth phosphate particles having a BET specific surface area of 10 to 200 m ² / g are used. By using rare earth phosphate particles having a BET specific surface area within this range, even if the particles are fine particles, the particles can be stably highly dispersed at a high concentration. In particular, the preferred BET specific surface area of the rare earth phosphate particles 20 to 200 m ² / g, more preferably 20~180m ² / g, even more preferably is 30~180m ² / g, a more highly particles High dispersion can be achieved more stably at the concentration.

In the present invention, the BET specific surface area can be measured by an N ₂ adsorption method using, for example, “Flowsorb 2300” manufactured by Shimadzu Corporation. The amount of the measured powder was 0.3 g, and the preliminary degassing conditions were 10 minutes at 120 ° C. under atmospheric pressure. Since the BET specific surface area of the rare earth phosphate particles dispersed in water cannot be measured, in the present invention, the rare earth phosphate particles remaining after the dispersion medium is removed from the aqueous dispersion are used. The BET specific surface area is measured as a measurement target. Also, the BET specific surface area of the raw rare earth phosphate particles used to prepare the aqueous dispersion of the present invention, and the BET specific surface area of the rare earth phosphate particles remaining after removing the dispersion medium from the aqueous dispersion The present inventors have confirmed that is substantially the same.

  By using the rare earth phosphate particles having the BET specific surface area, the aqueous dispersion of the present invention has a high concentration of 5 to 50% by mass of the particles. The preferred concentration is 5 to 40% by mass, the more preferred concentration is 5 to 30% by mass, the more preferred concentration is 5 to 20% by mass, and the still more preferred concentration is 7 to 15% by mass. Such a high concentration aqueous dispersion is advantageous in that, for example, when an optical lens is produced by application of the aqueous dispersion, a thin film having a desired thickness can be formed even if the number of times of application is reduced.

As will be described later, the aqueous dispersion of the present invention is highly transparent, and in order to make the aqueous dispersion transparent, the maximum particle size of the rare earth phosphate particles contained in the aqueous dispersion D _max is important. Specifically, the maximum particle size D _max of the rare earth phosphate particles needs to be 100 nm or less, preferably 70 nm or less, more preferably 60 nm or less. When the maximum particle size D _max exceeds 100 nm, the transparency of the aqueous dispersion is lowered due to the scattering of visible light. The lower limit of the maximum particle diameter _Dmax is not particularly limited, and the lower the better, the better. However, when the maximum particle diameter _Dmax is reduced to about 20 nm, the transparency of the aqueous dispersion becomes sufficiently high. The maximum particle diameter D _max of the rare earth phosphate particles is measured by a dynamic light scattering method using a photon correlation method. For example, it is measured using a nanotrack particle size distribution measuring device manufactured by Nikkiso Co., Ltd.

Where the maximum particle size D _max of the rare earth phosphate particles contained in the aqueous dispersion is as described above, it is preferred that the particles of the reduced volume average particle diameter D ₅₀ is 1～70Nm, is 1~40nm Is more preferable, and it is still more preferable that it is 5-40 nm. In addition to the maximum particle size D _max being in the above range, the average particle size D ₅₀ is in this range, thereby further improving the transparency of the aqueous dispersion. The average particle diameter D ₅₀ is measured by the maximum particle diameter D _max the same method.

  As the shape of the rare earth phosphate particles, for example, a spherical shape, a polyhedral shape, a needle shape or the like can be adopted. In particular, when the rare earth phosphate particles are spherical, when an optical lens is produced from the aqueous dispersion of the present invention containing the particles, birefringence is less likely to occur in the optical lens.

  The aqueous dispersion may further contain metal oxide particles having a high refractive index in addition to the rare earth phosphate particles. Examples of such metal oxides include Mg, Ca, Ti, Zn, Zr, Ta, Nb, Ga, Ge, Sn, In, Hf, Y, and lanthanoids (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and other metal oxides. These metal oxides can be used alone or in combination of two or more. These metal oxides can be used in an amount of about 0.1 to 50% by mass with respect to the entire particles as solids contained in the aqueous dispersion.

  The aqueous dispersion of the present invention is also characterized by high stability when stored for a long period of time. In order to increase the stability of the aqueous dispersion, the pH of the aqueous dispersion is set to a specific range on the acidic side or a specific range on the alkaline side. On the acidic side, the pH of the aqueous dispersion is set to 1 or more and less than 5, preferably 2 or more and less than 5, more preferably 2 or more and 4 or less. When the pH of the aqueous dispersion is less than 1 on the acidic side, the rare earth phosphate particles may be dissolved. When the pH is 5 or more, it is not easy to highly disperse the rare earth phosphate particles, and precipitation occurs when stored immediately or for a long time. For the alkaline side, the pH of the aqueous dispersion is set to 9.1 to 14, preferably 9.1 to 13.5, and more preferably 9.1 to 13. When the pH of the aqueous dispersion is less than 9.1 on the alkaline side, it is not easy to highly disperse the rare earth phosphate particles, and precipitation occurs when stored immediately or for a long time. When the pH exceeds 14, the particle surface may be altered by reaction with hydroxide ions. These pH values are values at temperatures during storage or use of the aqueous dispersion.

  In order to adjust the pH of the aqueous dispersion within the above range, a pH adjuster may be added to the aqueous dispersion. As the pH adjuster used on the acidic side, for example, various organic acids and inorganic acids can be used. Examples of the organic acid include acetic acid, formic acid and propionic acid. Examples of inorganic acids include hydrofluoric acid, nitric acid, hydrochloric acid, and sulfuric acid. These organic acids and inorganic acids can be used singly or in combination of two or more. As the pH adjuster used on the alkaline side, various hydroxides, alkylamines, aqueous ammonia and the like can be used. Examples of the hydroxide include tetraalkylammonium hydroxides such as tetramethylammonium hydroxide, and alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. As the alkylamine, any of monoalkylamine, dialkylamine and trialkylamine can be used depending on the ease of pH adjustment. As the alkyl group in the alkylamine, for example, the same or different lower alkyl group having 1 to 4 carbon atoms (such as a methyl group or an ethyl group) can be used. These hydroxides, alkylamines, aqueous ammonia and the like can be used singly or in combination of two or more. The amount of the above various pH adjusting agents added to the aqueous dispersion may be an amount such that the pH of the aqueous dispersion is in the above range.

  The aqueous dispersion preferably contains water as a medium, one or two or more rare earth phosphate particles as a medium, and contains other components as much as possible except that it contains a pH adjuster as necessary. In particular, it is desirable not to include solid components other than rare earth phosphate particles.

  The aqueous dispersion of the present invention is also characterized by being highly transparent in the visible light wavelength region (400 to 800 nm). In detail, when the transmittance in the wavelength region of visible light is measured using a cell having an optical path length of 1 cm, the transparency is preferably 50% or more, more preferably 80% or more, more preferably 90% or more. It is. Thus, when a coating film is formed using an aqueous dispersion having high transparency, the transparency of the coating film after drying becomes extremely high. Therefore, the aqueous dispersion of the present invention is very useful for the production of a transparent film having a high refractive index and low wavelength dispersion in the visible light wavelength region. A transparent film having a high refractive index and low wavelength dispersion in the visible light wavelength region contributes to a reduction in the thickness of optical lenses such as sheet lenses. The transparency of the aqueous dispersion can be measured by, for example, a spectrophotometer U-4000 manufactured by Hitachi High-Technology Corporation.

  In addition to having high transparency, the aqueous dispersion of the present invention is highly stable even after long-term storage. For example, it has a stability that does not cause precipitation even when stored for 1 month at room temperature.

  Next, the suitable manufacturing method of the aqueous dispersion liquid of this invention is demonstrated. This production method is roughly divided into (i) a process for producing rare earth phosphate particles and (ii) a process for producing an aqueous dispersion. Both of these steps will be described.

  First, the manufacturing process of the rare earth phosphate particles (i) will be described. Rare earth phosphate particles are produced by mixing an aqueous solution containing one or more rare earth elements and an aqueous solution containing orthophosphoric acid to cause precipitation of one or more rare earth phosphates. can get. This precipitation is subjected to a baking step as necessary to increase its crystallinity.

Mixing of an aqueous solution containing a rare earth element and an aqueous solution containing phosphoric acid includes the following aspects (a) and (b).
(A) An aqueous solution containing phosphoric acid is added to an aqueous solution containing a rare earth element.
(B) An aqueous solution containing a rare earth element is added to an aqueous solution containing phosphoric acid.
In any embodiment, aging is preferably performed after mixing. Aging time of 5 to 300 minutes is sufficient.

As the aqueous solution containing a rare earth element, one having a rare earth element concentration in the aqueous solution of 0.01 to 1.5 mol / liter, particularly 0.01 to 1 mol / liter, especially 0.01 to 0.5 mol / liter. It is preferable to use it. In this aqueous solution, the rare earth element is in a trivalent ion state or a complex ion state in which a ligand is coordinated to the trivalent ion. In order to prepare an aqueous solution containing a rare earth element, for example, a rare earth oxide (such as Ln ₂ O ₃ ) may be added to an aqueous nitric acid solution and dissolved.

  As the aqueous solution containing orthophosphoric acid, the total concentration of phosphoric acid species in the aqueous solution is 0.01 to 3 mol / liter, particularly 0.01 to 1 mol / liter, especially 0.01 to 0.5 mol / liter. It is preferable to do. Further, an alkali species can be added for pH adjustment. As the alkali species, for example, ammonia, ammonium hydrogen carbonate, ammonium carbonate, sodium hydrogen carbonate, sodium carbonate, ethylamine, propylamine, sodium hydroxide, potassium hydroxide and the like can be used.

  It is efficient that the aqueous solution containing the rare earth element and the aqueous solution containing phosphoric acid are mixed so that the molar ratio of phosphate ion / rare earth element ion is 0.5 to 10, particularly 1 to 10, especially 1 to 5. This is preferable in that a precipitated product is obtained.

  Even when any of the mixing methods (a) and (b) described above is employed, it is preferable that there is no substance that hinders the growth of the core particles produced by the reaction. When such a substance is present in the reaction system, the growth of the produced core particles is inhibited, the primary particle diameter of the obtained rare earth phosphate particles becomes excessively small, and the BET specific surface area becomes excessively large. An excessively small primary particle size is also advantageous in that the surface activity of the rare earth phosphate particles becomes excessively high, an unintentional dissolution and precipitation reaction occurs, and the stability in the dispersion decreases. I can not say. Examples of the substance that hinders the growth of the generated core particles include citric acid described in Patent Document 1. Citric acid is adsorbed on the surface of the produced core particles and inhibits the particles from becoming larger. As another aspect, the use of citric acid is not advantageous because BOD (Biochemical Oxygen Demand) in the waste liquid after the reaction becomes high and waste liquid treatment cannot be economically performed.

  The pH of the reaction system affects the form of the precipitated product for the reasons described below. The relationship between the mixing methods (a) and (b) described above and the pH of the reaction system is as follows. When the reaction is carried out in the mode (a), the reaction solution tends to change at a low pH. This is because the aqueous solution containing rare earth elements is acidic with pH <1. On the other hand, when the reaction is carried out in the mode (b), the pH of the reaction solution depends on the pH of the aqueous solution containing phosphoric acid, and when ammonia is used as the pH adjuster, the pH is adjusted within a pH range of 0.1 to 10. Is possible.

The form of phosphate ions changes with pH. In the reaction with rare earth element ions, the form of phosphate ions affects the precipitated product. For example, when ammonia is used as a pH adjuster, the presence of H ₂ PO ₄ ⁻ is dominant at pH <4. When the pH is 4 to 8, the presence of H ₂ PO ₄ ⁻ and HPO ₄ ²⁻ becomes dominant. At pH> 8, the presence of HPO ₄ ^2- and PO ₄ ^3- is dominant. In the reaction between rare earth element ions and phosphate ions, LnHPO ₄ is likely to be generated in the reaction between H ₂ PO ₄ ⁻ generated at low pH and rare earth element ions. On the other hand, LnPO ₄ is likely to be formed by the reaction between PO ₄ ³⁻ and rare earth element ions generated at high pH (Hisashi Naganaga, “Inorganic synthesis using solution as reaction field” Bafukan (2000)).

  The precipitated product also changes depending on the temperature at the time of mixing. From this viewpoint, the reaction temperature is preferably 20 to 100 ° C. As a general tendency, when the reaction temperature is increased, a crystalline rare earth phosphate is easily obtained and the crystallinity thereof is increased. When the crystallinity is high, the firing step described below is not necessary, so that the rare earth phosphate can be obtained by a simpler method. From the viewpoint of obtaining spherical particles, when mixing is performed in the mode (a), the reaction temperature is preferably 20 to 50 ° C.

  When the rare earth phosphate is obtained as described above, this is subjected to solid-liquid separation according to a conventional method and then washed with water once or a plurality of times. Washing with water is preferably performed until the electrical conductivity of the liquid reaches, for example, 2000 μS / cm or less.

  When the precipitated product is amorphous, it is preferable to perform calcination to make it crystalline. Firing can be performed in an oxygen-containing atmosphere such as the air. The firing condition in that case is preferably a firing temperature of 300 to 1000 ° C, more preferably 400 to 1000 ° C. By adopting this temperature range, it is possible to easily obtain rare earth phosphate particles having a target BET specific surface area. If the firing temperature is excessively high, sintering proceeds and the BET specific surface area of the particles tends to decrease. The firing time is preferably 1 to 20 hours, more preferably 1 to 10 hours, provided that the firing temperature is within this range.

The important point in this production method is the specific surface area of the rare earth phosphate particles used in the aqueous dispersion (ii). Specifically, BET specific surface area of preferably 10 to 200 m ² / g, more preferably 20 to 200 m ² / g, more preferably 20~180m ² / g, and even more preferably 30~180m ² / g rare earth Phosphate particles are provided for the preparation of the aqueous dispersion of (ii). This makes it possible to easily obtain an aqueous dispersion that can be highly dispersed at a high concentration, has high transparency, and is stable over a long period of time.

  When the precipitation product obtained by the reaction of an aqueous solution containing phosphoric acid and an aqueous solution containing a rare earth element has the above-mentioned BET specific surface area, use this as it is for the aqueous dispersion of (ii). Is advantageous. Although it is possible to use the phosphate compound subjected to the firing step described above in the aqueous dispersion of (ii), attention must be paid to the decrease in the BET specific surface area caused by firing. . If the conditions described above are employed as the firing conditions, it is easy to keep the BET specific surface area of the phosphate compound after firing within the above range.

  The specific surface area converted particle diameter of the rare earth phosphate particles having a BET specific surface area in the above-mentioned preferred range is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 20 nm or less.

  Next, the process for producing the aqueous dispersion (ii) will be described. In this step, crystalline or amorphous rare earth phosphate particles and water are mixed to form a slurry, and wet pulverization is performed by a media mill such as a bead mill. Examples of the beads to be used include zirconia beads and alumina beads. In this case, it is easy to bring the rare earth phosphate particles close to a monodispersed state by adding various pH adjusters to the slurry and performing a pulverization operation. As the pH adjuster, it is preferable to use one that can adjust the pH of the liquid to preferably 1 or more and less than 5, more preferably 2 or more and less than 5, and still more preferably 2 or more and 4 or less. As such a pH adjuster, for example, the organic acids and inorganic acids described above can be used. In addition, it is preferable to use a liquid whose pH can be adjusted to preferably 9.1 to 14, more preferably 9.1 to 13.5, and still more preferably 9.1 to 13. As such a pH adjuster, it is preferable to use, for example, the various hydroxides described above.

  The above pH adjuster may be added to the aqueous dispersion obtained by wet pulverization instead of adding it to the slurry during wet pulverization. When the pH adjuster is added to the aqueous dispersion, the added amount is such that the pH of the aqueous dispersion is preferably within the above-mentioned range. Note that a new surface is generated in the rare earth phosphate particles by wet pulverization, and the pH of the liquid may fluctuate as a result of the surface reacting with acid or alkali. Therefore, when adding a pH adjuster at the time of wet pulverization, it is preferable to determine the addition amount of the pH adjuster in anticipation of fluctuations in pH during wet pulverization.

  After the wet pulverization, the liquid and beads are separated, and the coarse particles are removed by a membrane filter to obtain the intended aqueous dispersion. The aqueous dispersion thus obtained is colorless and transparent and has a high visible light transmittance. Moreover, it is stable and does not cause precipitation even when stored for a long time.

  The aqueous dispersion obtained in this way is used for various optical materials by utilizing the high refractive index and low wavelength dispersibility of the rare earth phosphate contained therein and the transparency to visible light of the aqueous dispersion. And can be used for electronic materials. For example, it can be used for optical system parts such as lenses, antireflection films, infrared transmission films and the like. Specifically, an aqueous dispersion is applied to the surface of various substrates such as transparent substrates and lenses to form a coating film, and the coating film is dried to provide high transparency, high refractive index, and low wavelength. A thin film having dispersibility can be formed. The dried thin film may be fired as necessary under an inert atmosphere, an oxidizing atmosphere such as air, or a weakly reducing atmosphere (for example, a hydrogen-containing atmosphere having an explosion limit concentration or less). This thin film is useful for further increasing the refractive index of the lens or as a thin lens itself. Furthermore, the aqueous dispersion of the present invention is also suitably used as a raw material for resin lenses in which rare earth phosphate particles contained therein are dispersed in a resin.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass%”.

[Example 1]
(1) Production of lutetium phosphate particles Lutetium phosphate particles were produced according to the following steps 1) to 13). This step corresponds to (a) described above.
1) 370 g of water was weighed in a glass container and heated to 80 ° C.
2) 14.4 g of 85% nitric acid (manufactured by Wako) was added to 1).
3) 7.4 g of Lu ₂ O ₃ (manufactured by Nippon Yttrium Co., Ltd.) was added to 2), completely dissolved, and cooled to room temperature (25 ° C.).
4) 390 g of water, 5.26 g of 25% phosphoric acid, and 9.30 g of 25% ammonia water were added to another glass container. The pH of this aqueous solution was 11.1.
5) The solution of 4) was sequentially fed into the solution of 3). The pH of the reaction solution was 0.8 to 1.6. The temperature of the reaction solution was 25 ° C. A precipitate was formed by the reaction.
6) After the feed, aging was performed at 25 ° C. for 10 minutes.
7) The precipitate was washed by decantation washing until the conductivity of the supernatant was 100 μS / cm or less.
8) After washing, solid-liquid separation was performed by vacuum filtration.
9) 8) was dried in air at 120 ° C. for 5 hours to obtain a white powder.
10) 9) was calcined in the atmosphere at 800 ° C. for 5 hours.
11) When the XRD measurement of the baked powder obtained in 10) was performed, a tetragonal LuPO ₄ peak was confirmed. The XRD measurement results are shown in FIG.
12) When the specific surface area of the calcined powder obtained in 10) was measured, it was 42 m ² / g and the converted particle size was 22 nm. Further, when the fired powder was observed with a transmission electron microscope (TEM), the shape was spherical.
13) When the reflectance with respect to visible light of the baked powder obtained in 10) was measured, the absorption edge was near 200 nm, and the transparency in the visible light region was confirmed. The reflectance measurement result is shown in FIG. A spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation was used for the measurement.

(2) Production of aqueous dispersion In a 50 ml resin container, 2.0 g of LuPO ₄ particles obtained in 10) and 23 g of pure water were added to obtain a slurry, and then 1.2 g of acetic acid was added to the container. Then, the pH of the slurry was adjusted to 2.3. Further, 100 g of 0.1 mmφ zirconia beads were added, the container was sealed, and wet pulverization was performed with a paint shaker. Wet grinding was performed for 3 hours. Finally, the liquid was passed through a 0.2 μm membrane filter to remove coarse particles to obtain a target aqueous dispersion (sol) of lutetium phosphate particles. The pH of this aqueous dispersion was 2.5. The obtained aqueous dispersion was colorless and transparent. When this was irradiated with a red laser (wavelength 650 nm), the Tyndall phenomenon was observed, and it was confirmed that the lutetium phosphate particles were highly dispersed.

The obtained aqueous dispersion was scooped into a collodion film and observed with a transmission electron microscope (TEM). As a result, the primary particle diameter of the lutetium phosphate particles was 10 nm. Further, the maximum particle size D _max and the volume-converted average particle size D ₅₀ were measured using a nanotrack particle size distribution measuring device manufactured by Nikkiso Co., Ltd. The results are shown in Table 1.

A small amount of this aqueous dispersion was weighed out and dried at 200 ° C., the solid content concentration of the lutetium phosphate particles was 8.5%, and it was confirmed that a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed out and dried at 150 ° C. to measure the BET specific surface area of the remaining lutetium phosphate particles, which was 50 m ² / g. Furthermore, the transparency of the aqueous dispersion to visible light was measured using a spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation, and a quartz cell having an optical path length of 1 cm. The transmittance at 800 nm) was 83% or more (the lowest value was 83% at λ = 400 nm).

  When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, no precipitation was observed and it was confirmed that the highly dispersed state was maintained.

[Example 2]
Lutetium phosphate particles were produced according to the following steps 1) to 11). This step corresponds to (b) described above.
1) 370 g of water was weighed in a glass container and heated to 80 ° C.
2) 14.4 g of 85% nitric acid (manufactured by Wako) was added to 1).
3) 7.4 g of Lu ₂ O ₃ (manufactured by Japan Yttrium Co.) was added to 2), completely dissolved and cooled to room temperature (25 ° C.).
4) 380 g of water, 8.8 g of 25% phosphoric acid, and 16.6 g of 25% aqueous ammonia were added to another glass container. The pH of this aqueous solution was 9.6.
5) The solution of 3) was sequentially fed into the solution of 4). The temperature of the reaction solution was 25 ° C. The pH of the reaction solution was 9.6 to 7.4.
6) After the feed, aging was performed at 25 ° C. for 10 minutes.
7) The precipitate was washed by decantation washing until the supernatant conductivity was 100 μS / cm or less.
8) After washing, solid-liquid separation was performed by vacuum filtration.
9) 8) was dried in air at 120 ° C. for 5 hours to obtain a white powder. The XRD measurement result of this powder is shown in FIG. Although the XRD pattern is amorphous and the LuPO ₄ peak is not clearly observed, the contents of Lu and P were measured by ICP (Inductively Coupled Plasma Atomic Emission Spectrometer), and Lu: P = 1: 1.06. It was.
10) When the specific surface area of the powder obtained in 9) was measured, it was 125 m ² / g, and the converted particle size was 7 nm. When this powder was observed with TEM, the shape was spherical.
11) When the reflectance of the powder obtained in 10) was measured, the absorption edge was around 300 nm, and the transparency in the visible light region was confirmed. The reflectance measurement result is shown in FIG.

Using the obtained LuPO ₄ particles, an aqueous dispersion was obtained in the same manner as in Example 1. The pH of this aqueous dispersion was 2.4. The obtained aqueous dispersion was colorless and transparent. When this was irradiated with a red laser (wavelength 650 nm), the Tyndall phenomenon was observed, and it was confirmed that the lutetium phosphate particles were highly dispersed.

When the primary particle diameter of the lutetium phosphate particles in the obtained aqueous dispersion was measured in the same manner as in Example 1, it was 6 nm. Further, in the same manner as in Example 1, the maximum particle size D _max and the volume converted average particle size D ₅₀ were measured. The results are shown in Table 1.

A small amount of this aqueous dispersion was weighed out and dried at 200 ° C., the solid content concentration of the lutetium phosphate particles was 8.5%, and it was confirmed that a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed and dried at 150 ° C. to measure the BET specific surface area of the remaining lutetium phosphate particles, which was 130 m ² / g. Further, when the transparency of the aqueous dispersion to visible light was measured in the same manner as in Example 1, the transmittance in the wavelength region of visible light (wavelength 400 to 800 nm) was 87% or more (the minimum value was λ = 87% at 400 nm).

  Furthermore, when this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, no precipitation was observed, and it was confirmed that the highly dispersed state was maintained.

Example 3
1) The LuPO ₄ particles obtained in Example 2 were calcined in the atmosphere at 800 ° C. for 5 hours.
2) When the XRD measurement of the baked powder obtained in 1) was performed, a tetragonal LuPO ₄ peak was confirmed. The XRD measurement results are shown in FIG.
3) When the specific surface area of the calcined powder obtained in 1) was measured, it was 28 m ² / g and the converted particle size was 33 nm. When this powder was observed with TEM, the shape was spherical.
4) When the reflectance of the fired powder obtained in 1) was measured, the absorption edge was near 300 nm, and the transparency in the visible light region was confirmed. The reflectance measurement result is shown in FIG.

Using the obtained LuPO ₄ particles, an aqueous dispersion was obtained in the same manner as in Example 1. The pH of this aqueous dispersion was 2.6. The obtained aqueous dispersion was colorless and transparent. When this was irradiated with a red laser (wavelength 650 nm), the Tyndall phenomenon was observed, and it was confirmed that the lutetium phosphate particles were highly dispersed.

When the primary particle diameter of the lutetium phosphate particles in the obtained aqueous dispersion was measured in the same manner as in Example 1, it was 14 nm. Further, in the same manner as in Example 1, the maximum particle size D _max and the volume converted average particle size D ₅₀ were measured. The results are shown in Table 1.

A small amount of this aqueous dispersion was weighed and dried at 200 ° C., the solid content concentration of the lutetium phosphate particles was 8.4%, and it was confirmed that a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed out and dried at 150 ° C. to measure the BET specific surface area of the remaining lutetium phosphate particles, which was 35 m ² / g. Furthermore, when the transparency of this aqueous dispersion to visible light was measured in the same manner as in Example 1, the transmittance in the visible light wavelength region (wavelength 400 to 800 nm) was 81% or more (the minimum value was λ = 81% at 400 nm).

  Further, when this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, no precipitation was observed and it was confirmed that the highly dispersed state was maintained.

Example 4
Lutetium phosphate particles were produced according to the following steps 1) to 11). This step corresponds to (a) described above.
1) 370 g of water was weighed in a glass container and heated to 80 ° C.
2) To 1), 14.4 g of 85% nitric acid (manufactured by Wako) and 7.4 g of Lu ₂ O ₃ (manufactured by Japan Yttrium) were added and dissolved.
3) 380 g of water and 13.8 g of 25% phosphoric acid were added to another glass container. The pH of this aqueous solution was 1.4.
4) 3) was added to 2), and aging was performed for 1 hour at 80 ° C. The pH of the reaction solution was 0.4 to 0.7.
5) The precipitate was washed by decantation washing until the supernatant conductivity was 100 μS / cm or less.
6) After washing, solid-liquid separation was performed by vacuum filtration.
7) 6) was dried in air at 120 ° C. for 5 hours to obtain a white powder. When XRD measurement was performed on this powder, a tetragonal LuPO ₄ peak was confirmed.
8) When the specific surface area of the powder obtained in 7) was measured, it was 168 m ² / g, and the converted particle size was 5 nm. When this powder was observed with TEM, the shape was spherical. 9) When the reflectance of the powder obtained in 8) was measured, the absorption edge was near 200 nm, and the transparency in the visible light region was confirmed. The reflectance measurement results are shown in FIG.

Using the obtained LuPO ₄ particles, an aqueous dispersion was obtained in the same manner as in Example 1. The pH of this aqueous dispersion was 2.4. The obtained aqueous dispersion was colorless and transparent. When this was irradiated with a red laser (wavelength 650 nm), the Tyndall phenomenon was observed, and it was confirmed that the lutetium phosphate particles were highly dispersed.

When the primary particle diameter of the lutetium phosphate particles in the obtained aqueous dispersion was measured in the same manner as in Example 1, it was 5 nm. Further, in the same manner as in Example 1, the maximum particle size D _max and the volume converted average particle size D ₅₀ were measured. The results are shown in Table 1.

A small amount of this aqueous dispersion was weighed and dried at 200 ° C., the solid content concentration of the lutetium phosphate particles was 8.1%, and it was confirmed that a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed out and dried at 150 ° C. to measure the BET specific surface area of the remaining lutetium phosphate particles, which was 176 m ² / g. Furthermore, when the transparency of the aqueous dispersion to visible light was measured in the same manner as in Example 1, the transmittance in the visible light wavelength region (wavelength 400 to 800 nm) was 88% or more (the minimum value was λ = 88% at 400 nm).

  Further, when this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, no precipitation was observed and it was confirmed that the highly dispersed state was maintained.

Example 5
1) The powder obtained in Example 4 was calcined in air at 800 ° C. for 5 hours.
2) When the XRD measurement of the baked powder obtained in 1) was performed, a tetragonal LuPO ₄ peak was confirmed. The XRD measurement results are shown in FIG.
3) When the specific surface area of the baked powder obtained in 1) was measured, it was 51 m ² / g, and the converted particle size was 18 nm. When this powder was observed with TEM, the shape was spherical.
4) When the reflectance of the fired powder obtained in 1) was measured, the absorption edge was near 200 nm, and the transparency in the visible light region was confirmed. The reflectance measurement result is shown in FIG.

Using the obtained LuPO ₄ particles, an aqueous dispersion was obtained in the same manner as in Example 1. The pH of this aqueous dispersion was 2.3. The obtained aqueous dispersion was colorless and transparent. When this was irradiated with a red laser (wavelength 650 nm), the Tyndall phenomenon was observed, and it was confirmed that the lutetium phosphate particles were highly dispersed.

When the primary particle diameter of the lutetium phosphate particles in the obtained aqueous dispersion was measured in the same manner as in Example 1, it was 10 nm. Further, in the same manner as in Example 1, the maximum particle size D _max and the volume converted average particle size D ₅₀ were measured. The results are shown in Table 1.

A small amount of this aqueous dispersion was weighed and dried at 200 ° C., the solid content concentration of the lutetium phosphate particles was 7.5%, and it was confirmed that a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed out and dried at 150 ° C. to measure the BET specific surface area of the remaining lutetium phosphate particles, which was 60 m ² / g. Furthermore, when the transparency of the aqueous dispersion to visible light was measured in the same manner as in Example 1, the transmittance in the wavelength region of visible light (wavelength 400 to 800 nm) was 84% or more (the minimum value was λ = 84% at 400 nm).

  Furthermore, when this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, no precipitation was observed, and it was confirmed that the highly dispersed state was maintained.

Example 6
The steps 1) to 10) of Example 1 were performed to obtain LuPO ₄ particles. The obtained LuPO ₄ particles (3.0 g) and 1% tetramethylammonium hydroxide aqueous solution (26 g) were placed in a 50 mL resin container to obtain a slurry having a pH of 12.5. Further, 100 g of 0.1 mmφ zirconia beads were added and wet pulverized by a paint shaker. Wet grinding was performed for 3 hours. The pH of the slurry after wet pulverization dropped to 9.1. Finally, the slurry was passed through a 0.2 μm membrane filter to remove coarse particles to obtain the desired aqueous dispersion (sol) of lutetium phosphate particles. The obtained aqueous dispersion was colorless and transparent. When this was irradiated with a red laser (wavelength 650 nm), the Tyndall phenomenon was observed, and it was confirmed that the lutetium phosphate particles were highly dispersed.

When the primary particle diameter of the lutetium phosphate particles in the obtained aqueous dispersion was measured in the same manner as in Example 1, it was 10 nm. Further, in the same manner as in Example 1, the maximum particle size D _max and the volume converted average particle size D ₅₀ were measured. The results are shown in Table 1.

A small amount of this aqueous dispersion was measured and dried at 200 ° C., the solid content concentration was 11.7%, and a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed out and dried at 150 ° C. to measure the BET specific surface area of the remaining lutetium phosphate particles, which was 45 m ² / g. Further, when the transparency of the aqueous dispersion to visible light was measured in the same manner as in Example 1, the transmittance in the wavelength region of visible light (wavelength 400 to 800 nm) was 87% or more (the minimum value was λ = 87% at 400 nm). The transmittance measurement results are shown in FIG.

  When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and examined for storage stability, no precipitate was observed and it was confirmed that the highly dispersed state was maintained.

Example 7
The steps 1) to 10) of Example 1 were performed to obtain LuPO ₄ particles. The obtained LuPO ₄ particles (3.0 g) and 2% tetramethylammonium hydroxide aqueous solution (21 g) were placed in a 50 mL resin container to obtain a slurry having a pH of 12.8. Further, 100 g of 0.1 mmφ zirconia beads were added and wet pulverized by a paint shaker. Wet grinding was performed for 3 hours. The pH of the slurry after wet grinding was lowered to 10.2. Finally, the slurry was passed through a 0.2 μm membrane filter to remove coarse particles to obtain the desired aqueous dispersion (sol) of lutetium phosphate particles. The obtained aqueous dispersion was colorless and transparent. When this was irradiated with a red laser (wavelength 650 nm), the Tyndall phenomenon was observed, and it was confirmed that the lutetium phosphate particles were highly dispersed.

When the primary particle diameter of the lutetium phosphate particles in the obtained aqueous dispersion was measured in the same manner as in Example 1, it was 10 nm. Further, in the same manner as in Example 1, the maximum particle size D _max and the volume converted average particle size D ₅₀ were measured. The results are shown in Table 1.

A small amount of this aqueous dispersion was measured and dried at 200 ° C., the solid content concentration was 12.2%, and a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed and dried at 150 ° C. to measure the BET specific surface area of the remaining lutetium phosphate particles, which was 47 m ² / g. Furthermore, when the transparency of the aqueous dispersion to visible light was measured in the same manner as in Example 1, the transmittance in the visible light wavelength region (wavelength 400 to 800 nm) was 88% or more (the minimum value was λ = 88% at 400 nm). The transmittance measurement results are shown in FIG.

  When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and examined for storage stability, no precipitate was observed and it was confirmed that the highly dispersed state was maintained.

Example 8
The steps 1) to 10) of Example 1 were performed to obtain LuPO ₄ particles. The obtained LuPO ₄ particles (3.0 g) and 5% tetramethylammonium hydroxide aqueous solution (21 g) were put in a 50 mL resin container to obtain a slurry having a pH of 13.1. Further, 100 g of 0.1 mmφ zirconia beads were added and wet pulverized by a paint shaker. Wet grinding was performed for 3 hours. The pH of the slurry after wet pulverization dropped to 12.2. Finally, the slurry was passed through a 0.2 μm membrane filter to remove coarse particles to obtain the desired aqueous dispersion (sol) of lutetium phosphate particles. The obtained aqueous dispersion was colorless and transparent. When this was irradiated with a red laser (wavelength 650 nm), the Tyndall phenomenon was observed, and it was confirmed that the lutetium phosphate particles were highly dispersed.

When the primary particle diameter of the lutetium phosphate particles in the obtained aqueous dispersion was measured in the same manner as in Example 1, it was 10 nm. Further, in the same manner as in Example 1, the maximum particle size D _max and the volume converted average particle size D ₅₀ were measured. The results are shown in Table 1.

A small amount of this aqueous dispersion was measured and dried at 200 ° C., the solid content concentration was 12.5%, and a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed out and dried at 150 ° C. to measure the BET specific surface area of the remaining lutetium phosphate particles. As a result, it was 43 m ² / g. Furthermore, when the transparency of the aqueous dispersion to visible light was measured in the same manner as in Example 1, the transmittance in the wavelength region of visible light (wavelength 400 to 800 nm) was 89% or more (the minimum value was λ = 89% at 400 nm).

  When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and examined for storage stability, no precipitate was observed and it was confirmed that the highly dispersed state was maintained.

[Comparative Example 1]
LuPO ₄ particles were obtained in the same manner as in Example 1 except that the firing conditions in Example 1 were 1200 ° C. × 3 hours in the air. The same measurement as in Example 1 was performed on the obtained particles. The results are shown in Table 1. Further, an aqueous dispersion was obtained in the same manner as in Example 1 using the obtained particles. The obtained aqueous dispersion was subjected to the same measurement as in Example 1. The results are shown in Table 1. This aqueous dispersion was cloudy, and precipitation was observed immediately, confirming that the storage stability was poor.

  As is apparent from the results shown in Table 1 and FIGS. 2 to 5, the aqueous dispersions obtained in each example are of high concentration, have high transparency, and generate precipitates even after storage for 1 month. Is not observed, indicating that the highly dispersed state is maintained. The particles could not be dispersed with the aqueous dispersion obtained in Comparative Example 1.

Example 9
(1) Production of ytterbium phosphate particles 1) 380 g of water was weighed into a glass container and heated to 80 ° C.
2) 14.4 g of 85% nitric acid (manufactured by Wako) was added to 1).
3) 7.5 g of Yb ₂ O ₃ (manufactured by Japan Yttrium Co.) was added to 2), completely dissolved, and cooled to room temperature (25 ° C.).
4) 390 g of water, 5.26 g of 25% phosphoric acid, and 9.30 g of 25% ammonia water were added to another glass container. The pH of this aqueous solution was 9.6.
5) The solution of 4) was sequentially fed into the solution of 3) at 25 ° C. The pH of the reaction solution was 1.2 to 2.3. A precipitate was formed by the reaction.
6) Aging was performed for 10 minutes at 25 ° C. after the feed was completed.
7) The precipitate was washed by decantation washing until the supernatant conductivity reached 100 μS / cm.
8) After washing, solid-liquid separation was performed by vacuum filtration.
9) 8) was dried in air at 120 ° C. for 5 hours to obtain a white powder.
10) 9) was calcined in air at 800 ° C. for 5 hours.
11) When the XRD measurement of the baked powder obtained in 10) was performed, a tetragonal YbPO ₄ peak was confirmed. The XRD measurement results are shown in FIG.
12) When the specific surface area of the calcined powder obtained in 10) was measured, it was 42 m ² / g and the converted particle size was 22 nm. Further, when the fired powder was observed with a transmission electron microscope (TEM), the shape was spherical.
13) When the reflectance with respect to visible light of the baked powder obtained in 10) was measured, the absorption edge was near 200 nm, and the transparency in the visible light region was confirmed. The reflectance measurement results are shown in FIG. A spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation was used for the measurement.

(2) Production of aqueous dispersion In a 50 ml resin container, 3.0 g of YbPO ₄ particles obtained in 10) and 21 g of 2% tetramethylammonium hydroxide aqueous solution were added to bring the pH of the slurry to 12.2. It was adjusted. Furthermore, 100 g of 0.1 mmΦ zirconia beads were added, and wet pulverization was performed with a paint shaker. Wet grinding was performed for 3 hours. Finally, the liquid was passed through a 0.2 μm membrane filter to remove coarse particles to obtain a target aqueous dispersion (sol) of ytterbium phosphate particles. When this was irradiated with a red laser (wavelength 650 nm), a Tyndall phenomenon was observed, and it was confirmed that the ytterbium phosphate particles were highly dispersed.

The obtained aqueous dispersion was scooped into a collodion film and observed with a transmission electron microscope (TEM). As a result, the primary particle diameter of the ytterbium phosphate particles was 13 nm. Further, the maximum particle size D _max and the volume-converted average particle size D ₅₀ were measured using a nanotrack particle size distribution measuring device manufactured by Nikkiso Co., Ltd. The results are shown in Table 2.

When this aqueous dispersion was weighed out and dried at 200 ° C., the solid content concentration of the ytterbium phosphate particles was 11.1%, and a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed out and dried at 150 ° C. to measure the BET specific surface area of the remaining ytterbium phosphate particles, which was 48 m ² / g. Furthermore, the transparency of the aqueous dispersion to visible light was measured using a spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation, and a quartz cell having an optical path length of 1 cm. The transmittance at (400 to 800 nm) was 84% or more (the minimum value was 84% at λ = 400 nm).

  When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, no precipitation was observed and it was confirmed that the highly dispersed state was maintained.

Example 10
(1) Production of Yttrium Phosphate Particles 1) 370 g of water was weighed into a glass container and heated to 80 ° C.
2) 20.4 g of 85% nitric acid (manufactured by Wako) was added to 1).
3) 6.1 g of Y ₂ O ₃ (manufactured by Kanto Chemical Co., Inc.) was added to 2), completely dissolved, and cooled to room temperature (25 ° C.).
4) 380 g of water, 7.5 g of 25% phosphoric acid, and 13.2 g of 25% aqueous ammonia were added to another glass container. The pH of this aqueous solution was 8.9.
5) The solution of 4) was sequentially fed into the solution of 3) at 25 ° C. The pH of the reaction solution was 1.5 to 1.9. A precipitate was formed by the reaction.
6) Aging was performed for 10 minutes at 25 ° C. after the feed was completed.
7) The precipitate was washed by decantation washing until the supernatant had a conductivity of 100 μS / cm or less.
8) After washing, solid-liquid separation was performed by vacuum filtration.
9) 8) was dried in air at 120 ° C. for 5 hours to obtain a white powder.
10) 9) was calcined in air at 800 ° C. for 5 hours.
11) When the XRD measurement of the baked powder obtained in 10) was performed, a tetragonal YPO ₄ peak was confirmed. The XRD measurement results are shown in FIG.
12) When the specific surface area of the baked powder obtained in 10) was measured, it was 63 m ² / g, and the converted particle size was 22 nm. Further, when the fired powder was observed with a transmission electron microscope (TEM), the shape was spherical.
13) When the reflectance with respect to visible light of the baked powder obtained in 10) was measured, the absorption edge was near 200 nm, and the transparency in the visible light region was confirmed. The reflectance measurement results are shown in FIG. A spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation was used for the measurement.

(2) Production of aqueous dispersion To a 50 mL resin container, 3.0 g of YPO ₄ particles obtained in 10) and 21 g of 2% tetramethylammonium hydroxide aqueous solution were added to make the pH of the slurry 12.8. It was adjusted. Furthermore, 100 g of 0.1 mmΦ zirconia beads were added, and wet pulverization was performed with a paint shaker. Wet grinding was performed for 3 hours. Finally, the liquid was passed through a 0.2 μm membrane filter to remove coarse particles to obtain a target aqueous dispersion (sol) of yttrium phosphate particles. When this was irradiated with a red laser (wavelength 650 nm), a Tyndall phenomenon was observed, and it was confirmed that yttrium phosphate particles were highly dispersed.

The obtained aqueous dispersion was scooped into a collodion film and observed with a transmission electron microscope (TEM). As a result, the primary particle diameter of the yttrium phosphate particles was 11 nm. Further, the maximum particle size D _max and the volume-converted average particle size D ₅₀ were measured using a nanotrack particle size distribution measuring device manufactured by Nikkiso Co., Ltd. The results are shown in Table 2.

When this aqueous dispersion was weighed out and dried at 200 ° C., the solid content concentration of the yttrium phosphate particles was 12.7%, and a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed out and dried at 150 ° C. to measure the BET specific surface area of the remaining yttrium phosphate particles, which was 69 m ² / g. Furthermore, the transparency of the aqueous dispersion to visible light was measured using a spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation, and a quartz cell having an optical path length of 1 cm. The transmittance at 400 to 800 nm was 85% or more (the minimum value was 85% at λ = 400 nm).

  When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, no precipitation was observed and it was confirmed that the highly dispersed state was maintained.

Example 11
(1) Production of gadolinium phosphate particles 1) 380 g of water was weighed into a glass container and heated to 80 ° C.
2) 15.0 g of 85% nitric acid (manufactured by Wako) was added to 1).
3) 7.2 g of Gd ₂ O ₃ (manufactured by Kanto Chemical Co., Inc.) was added to 2), completely dissolved, and cooled to room temperature (25 ° C.).
4) To another glass container, 390 g of water, 5.5 g of 25% phosphoric acid, and 9.7 g of 25% aqueous ammonia were added. The pH of this aqueous solution was 9.3.
5) The solution of 4) was sequentially fed into the solution of 3) at 25 ° C. The pH of the reaction solution was 1.3 to 2.1. A precipitate was formed by the reaction.
6) After ending Ford, aging was performed for 10 minutes at 25 ° C.
7) The precipitate was washed by decantation washing until the supernatant had a conductivity of 100 μS / cm or less.
8) After washing, solid-liquid separation was performed by vacuum filtration.
9) 8) was dried in air at 120 ° C. for 5 hours to obtain a white powder.
10) 9) was calcined in air at 800 ° C. for 5 hours.
11) When XRD measurement of the calcined powder obtained in 10) was performed, a monoclinic GdPO ₄ peak was confirmed. The XRD measurement results are shown in FIG.
12) When the specific surface area of the calcined powder obtained in 10) was measured, it was 28 m ² / g and the converted particle size was 36 nm. Further, when the fired powder was observed with a transmission electron microscope (TEM), the shape was spherical.
13) When the reflectance with respect to visible light of the baked powder obtained in 10) was measured, the absorption edge was near 200 nm, and the transparency in the visible light region was confirmed. The reflectance measurement results are shown in FIG. A spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation was used for the measurement.

(2) Production of aqueous dispersion In a 50 mL resin container, 1.8 g of GdPO ₄ particles obtained in 10) and 21 g of 2% tetramethylammonium hydroxide aqueous solution were added to make the pH of the slurry 12.8. It was adjusted. Furthermore, 100 g of 0.1 mmΦ zirconia beads were added, and wet pulverization was performed with a paint shaker. Wet grinding was performed for 3 hours. Finally, the liquid was passed through a 0.2 μm membrane filter to remove coarse particles to obtain a target aqueous dispersion (sol) of gadolinium phosphate particles. When this was irradiated with a red laser (wavelength 650 nm), the Tyndall phenomenon was observed, and it was confirmed that the gadolinium phosphate particles were highly dispersed.

The obtained aqueous dispersion was scooped into a collodion film and observed with a transmission electron microscope (TEM). As a result, the primary particle diameter of the gadolinium phosphate particles was 18 nm. Further, the maximum particle size D _max and the volume-converted average particle size D ₅₀ were measured using a nanotrack particle size distribution measuring device manufactured by Nikkiso Co., Ltd. The results are shown in Table 2.

When this aqueous dispersion was weighed out and dried at 200 ° C., the gadolinium phosphate particles had a solid content concentration of 5.5%, and a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed out and dried at 150 ° C. to measure the BET specific surface area of the remaining gadolinium phosphate particles, which was 30 m ² / g. Furthermore, the transparency of the aqueous dispersion to visible light was measured using a spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation, and a quartz cell having an optical path length of 1 cm. The transmittance at 400 to 800 nm was 86% or more (the minimum value was 86% at λ = 400 nm).

  When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, no precipitation was observed and it was confirmed that the highly dispersed state was maintained.

Example 12
(1) Production of lanthanum phosphate particles 1) 380 g of water was weighed into a glass container and heated to 80 ° C.
2) 16.3 g of 85% nitric acid (manufactured by Wako) was added to 1).
3) 7.0 g of La ₂ O ₃ (manufactured by Kanto Chemical Co., Inc.) was added to 2), completely dissolved, and cooled to room temperature (25 ° C.).
4) To another glass container, 390 g of water, 6.0 g of 25% phosphoric acid and 10.5 g of 25% aqueous ammonia were added. The pH of this aqueous solution was 9.6.
5) The solution of 4) was sequentially fed into the solution of 3) at 25 ° C. The pH of the reaction solution was 1.2 to 2.1. A precipitate was formed by the reaction.
6) After ending Ford, aging was performed for 10 minutes at 25 ° C.
7) The precipitate was washed by decantation washing until the supernatant had a conductivity of 100 μS / cm or less.
8) After washing, solid-liquid separation was performed by vacuum filtration.
9) 8) was dried in air at 120 ° C. for 5 hours to obtain a white powder.
10) 9) was calcined in air at 800 ° C. for 5 hours.
11) When XRD measurement was performed on the calcined powder obtained in 10), a monoclinic LaPO ₄ peak was confirmed. The XRD measurement results are shown in FIG.
12) When the specific surface area of the baked powder obtained in 10) was measured, it was 32 m ² / g and the converted particle size was 37 nm. Further, when the fired powder was observed with a transmission electron microscope (TEM), the shape was spherical.
13) When the reflectance with respect to visible light of the baked powder obtained in 10) was measured, the absorption edge was near 200 nm, and the transparency in the visible light region was confirmed. The reflectance measurement result is shown in FIG. A spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation was used for the measurement.

(2) Production of aqueous dispersion To a 50 mL resin container, 1.8 g of LaPO ₄ particles obtained in 10) and 21 g of 2% tetramethylammonium hydroxide aqueous solution are added to make the pH of the slurry 12.8. It was adjusted. Furthermore, 100 g of 0.1 mmΦ zirconia beads were added, and wet pulverization was performed with a paint shaker. Wet grinding was performed for 3 hours. Finally, the liquid was passed through a 0.2 μm membrane filter to remove coarse particles to obtain a target aqueous dispersion (sol) of lanthanum phosphate particles. When this was irradiated with a red laser (wavelength 650 nm), a Tyndall phenomenon was observed, and it was confirmed that the lanthanum phosphate particles were highly dispersed.

The obtained aqueous dispersion was scooped into a collodion film and observed with a transmission electron microscope (TEM). As a result, the primary particle diameter of the lanthanum phosphate particles was 17 nm. Further, the maximum particle size D _max and the volume-converted average particle size D ₅₀ were measured using a nanotrack particle size distribution measuring device manufactured by Nikkiso Co., Ltd. The results are shown in Table 2.

When this aqueous dispersion was weighed out and dried at 200 ° C., the solid content concentration was 10.2%, and a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed out and dried at 150 ° C. to measure the BET specific surface area of the remaining lanthanum phosphate particles, which was 35 m ² / g. Furthermore, the transparency of the aqueous dispersion to visible light was measured using a spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation, and a quartz cell having an optical path length of 1 cm. The transmittance at 400 to 800 nm was 87% or more (the minimum value was 87% at λ = 400 nm).

  When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, no precipitation was observed and it was confirmed that the highly dispersed state was maintained.

Example 13
After adding 1.8 g of LuPO ₄ particles obtained in Example 1 and 21 g of water to a 50 mL resin container, the pH of the slurry was adjusted to 4.0 using acetic acid. Further, 100 g of 0.1 mmΦ zirconia beads were added, and wet pulverization was performed with a paint shaker. Wet grinding was performed for 3 hours. Finally, the liquid was passed through a 0.2 μm membrane filter to remove coarse particles to obtain a target aqueous dispersion (sol) of lutetium phosphate particles. When this was irradiated with a red laser (wavelength 650 nm), the Tyndall phenomenon was observed, and it was confirmed that the lutetium phosphate particles were highly dispersed.

The obtained aqueous dispersion was scooped into a collodion film and observed with a transmission electron microscope (TEM). As a result, the primary particle diameter of the lutetium phosphate particles was 10 nm. Further, the maximum particle size D _max and the volume-converted average particle size D ₅₀ were measured using a nanotrack particle size distribution measuring device manufactured by Nikkiso Co., Ltd. The results are shown in Table 2.

When this aqueous dispersion was weighed out and dried at 200 ° C., the solid concentration was 9.2%, and a glassy transparent solid remained. Further, 2 g of the aqueous dispersion was weighed and dried at 150 ° C. to measure the BET specific surface area of the remaining lutetium phosphate particles, which was 47 m ² / g. Furthermore, the transparency of the aqueous dispersion to visible light was measured using a spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation, and a quartz cell having an optical path length of 1 cm. The transmittance at 400 to 800 nm was 82% or more. (The minimum value is 82% at λ = 400 nm)

  When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, no precipitation was observed and it was confirmed that the highly dispersed state was maintained.

Example 14
After adding 6.5 g of LuPO ₄ particles obtained in Example 1 and 21 g of water to a 50 mL resin container, the pH of the slurry was adjusted to 2.0 using acetic acid. Further, 100 g of 0.1 mmΦ zirconia beads were added, and wet pulverization was performed with a paint shaker. Wet grinding was performed for 3 hours. Finally, the liquid was passed through a 0.2 μm membrane filter to remove coarse particles to obtain a target aqueous dispersion (sol) of lutetium phosphate particles. When this was irradiated with a red laser (wavelength 650 nm), the Tyndall phenomenon was observed, and it was confirmed that the lutetium phosphate particles were highly dispersed.

The obtained aqueous dispersion was scooped into a collodion film and observed with a transmission electron microscope (TEM). As a result, the primary particle diameter of the lutetium phosphate particles was 10 nm. Further, the maximum particle size D _max and the volume-converted average particle size D ₅₀ were measured using a nanotrack particle size distribution measuring device manufactured by Nikkiso Co., Ltd. The results are shown in Table 2.

When this aqueous dispersion was weighed out and dried at 200 ° C., the solid content concentration was 30.2%, and a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed out and dried at 150 ° C. to measure the BET specific surface area of the remaining lutetium phosphate particles, which was 51 m ² / g. Furthermore, the transparency of the aqueous dispersion to visible light was measured using a spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation, and a quartz cell having an optical path length of 1 cm. The transmittance in the range of 400 to 800 nm was 68% or more (the minimum value was 68% at λ = 400 nm).

  When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, no precipitation was observed and it was confirmed that the highly dispersed state was maintained.

Example 15
After adding 2.0 g of the GdPO ₄ particles obtained in Example 11 and 21 g of water to a 50 mL resin container, the pH of the slurry was adjusted to 2.8 using acetic acid. Further, 100 g of 0.1 mmφ zirconia beads were added, and wet pulverization was performed with a paint shaker. Wet grinding was performed for 3 hours. Finally, the liquid was passed through a 0.2 μm membrane filter to remove coarse particles to obtain a target aqueous dispersion (sol) of gadolinium phosphate particles. When this was irradiated with a red laser (wavelength 650 nm), the Tyndall phenomenon was observed, and it was confirmed that the gadolinium phosphate particles were highly dispersed.

The obtained aqueous dispersion was scooped into a collodion film and observed with a transmission electron microscope (TEM). As a result, the primary particle diameter of the gadolinium phosphate particles was 18 nm. Further, the maximum particle size D _max and the volume-converted average particle size D ₅₀ were measured using a nanotrack particle size distribution measuring device manufactured by Nikkiso Co., Ltd. The results are shown in Table 2.

A small amount of this aqueous dispersion was weighed and dried at 200 ° C., the solid content concentration was 8.5%, and a glassy transparent solid content remained. Further, 2 g of the aqueous dispersion was weighed and dried at 150 ° C. to measure the remaining gadolinium phosphate particles. The BET specific surface area was measured and found to be 32 m ² / g. Furthermore, the transparency of the aqueous dispersion to visible light was measured using a spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation, and a quartz cell having an optical path length of 1 cm. The transmittance at 800 nm) was 87% or more. (The minimum value is 87% at λ = 400 nm)

  When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and examined for storage stability, no precipitate was observed and it was confirmed that the highly dispersed state was maintained.

[Comparative Example 2]
In this comparative example, the pH of the aqueous dispersion is set near neutral. To a 50 mL resin container, 2.0 g of LuPO ₄ particles obtained in Example 1 and 21 g of water were added. The pH of the slurry was 6.7. Further, 100 g of 0.1 mmΦ zirconia beads were added, and wet pulverization was performed with a paint shaker. Although the wet pulverization was performed for 3 hours, a highly dispersed liquid was not obtained. Therefore, the primary particle size, the maximum particle size D _max , the volume conversion average particle size D ₅₀ , the BET specific surface area and the minimum visible light transmittance could not be measured.

  As is clear from the results shown in Table 2 and FIGS. 6 to 10, the aqueous dispersions obtained in each example are of high concentration, have high transparency, and generate precipitates even after storage for 1 month. Is not observed, indicating that the highly dispersed state is maintained. The particles could not be dispersed with the aqueous dispersion obtained in Comparative Example 2.

Claims (7)

An aqueous dispersion containing particles of a rare earth phosphate having a BET specific surface area of 10 to 200 m ² / g, wherein the maximum particle diameter D _{max of the} particles is 100 nm or less, and the pH of the aqueous dispersion is 1 An aqueous dispersion having a particle concentration of 5 to 50% by mass. An aqueous dispersion containing particles of a rare earth phosphate having a BET specific surface area of 10 to 200 m ² / g, wherein the maximum particle diameter D _{max of the} particles is 100 nm or less, and the pH of the aqueous dispersion is 9 An aqueous dispersion having a particle concentration of 1 to 14 and a concentration of the particles of 5 to 50% by mass.   The aqueous dispersion according to claim 1 or 2, wherein the transmittance in the wavelength region of visible light is 50% or more when measured using a cell having an optical path length of 1 cm. Aqueous dispersion according to any one of 3 to terms of volume-average particle diameter D ₅₀ of the particles claims 1 is 1～70Nm. A method for producing an aqueous dispersion according to claim 1,
A method for producing an aqueous dispersion, wherein particles comprising a rare earth phosphate having a BET specific surface area of 10 to 200 m ² / g are dispersed in an aqueous medium, and the pH is adjusted to 1 or more and less than 5. A method for producing an aqueous dispersion according to claim 2,
A method for producing an aqueous dispersion, wherein particles comprising a rare earth phosphate having a BET specific surface area of 10 to 200 m ² / g are dispersed in an aqueous medium, and the pH is adjusted to 9.1 or more and 14 or less.   A method for producing a transparent thin film, comprising applying the aqueous dispersion according to any one of claims 1 to 4 to a surface of a substrate to form a coating film, and drying the coating film.

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